1. Field of the Invention
The present invention relates generally to those apparatus and methods wherein a subject vapor is absorbed within an absorbent liquid by direct contact therebetween, accompanied by removal of the heat of absorption from such apparatus or method. The field to which applicants' invention has application is further restricted to those apparatus and methods described wherein an additive is included which exists in at least a vapor phase concurrently with the subject vapor, which additive is effective to reduce the surface tension of the absorbent liquid upon contact therewith. In a specific application, the invention relates to an absorption refrigeration system of the type utilizing an aqueous solution of lithium bromide as the absorbent solution and water as the refrigerant, wherein an octyl alcohol additive is provided in order to increase the performance of the system.
2. Description of the Prior Art
In the technical literature dealing with the theoretical aspects of mass transfer, numerous articles appear which discuss the importance of interfacial turbulence between phases which serves to enhance or promote the mass transfer mechanism. Interfacial turbulence may exist both with respect to liquid/liquid interfaces and liquid/vapor interfaces, the latter being relevant to the present discussion.
A textbook entitled, Mass Transfer by Sherwood, Pigford, and Wilke (McGraw-Hill, 1975) contains a discussion of interfacial turbulence from pages 184 through 188. In this discussion, the authors observe that abnormally high mass transfer rates occur in those apparatus and methods wherein marked interfacial turbulence is present. They go on to attribute this phenomenon to the "Marangoni effect", a term applied to instability which develops within a film of liquid due to random variations in surface tension at the film interface. This instability generates ripples and "roll cells" to cause liquid circulation within the film between its surface and bulk. The authors attribute the presence of the instability within the liquid film to the fact that, as mass transfer occurs, local concentrations develop which result in variations in surface tension of the liquid.
It has been known for many years to those skilled in the art of absorption refrigeration that the performance and capacity of an absorption refrigeration system of the type utilizing an aqueous solution of lithium bromide as the absorbent and water as the refrigerant, may be increased by the addition of certain additives such as octyl alcohol (2 ethyl-n-hexanol). A brief discussion of this concept appears in U.S. Pat. No. 3,276,217. This increase in performance has been attributed to a number of factors, including the creation of a turbulent film on the exterior surfaces of the absorber tubes, resulting in better heat transfer between the film and the tubes. It is further suggested that the addition of octyl alcohol effects dropwise condensation of refrigerant vapor in the condenser, resulting in improved heat transfer in that part of the system. U.S. Pat. No. 3,593,540 also discusses the improved results obtained through the addition of octyl alcohol to a lithium bromide absorption refrigeration system, attributing such improved results to increased heat transfer in both the absorber and condenser.